1. Field
The present disclosure is directed to additive compositions and lubricants containing oxazoline derivatives. In particular, it is directed to additive compositions and lubricants containing hydrocarbyl oxazolines as friction modifiers for reducing thin film friction and/or boundary layer friction.
2. Description of the Related Technology
To ensure smooth operation of engines, engine oils play an important role in lubricating a variety of sliding parts in the engine, for example, piston rings/cylinder liners, bearings of crankshafts and connecting rods, valve mechanisms including cams and valve lifters, and the like. Engine oils may also play a role in cooling the inside of an engine and dispersing combustion products. Further possible functions of engine oils may include preventing or reducing rust and corrosion.
The principle consideration for engine oils is to prevent wear and seizure of parts in the engine. Lubricated engine parts are mostly in a state of fluid lubrication, but valve systems and top and bottom dead centers of pistons are likely to be in a state of boundary lubrication. The friction between these parts in the engine may cause significant energy losses and thereby reduce fuel efficiency. Many types of friction modifiers have been used in engine oils to decrease frictional energy losses.
Improved fuel efficiency may be achieved when friction between engine parts is reduced. Thin-film friction is the friction generated by a fluid, such as a lubricant, moving between two surfaces, when the distance between the two surfaces is very small. It is known that some additives normally present in engine oils form films of different thicknesses, which can have an effect on thin-film friction. Some additives, such as zinc dialkyl dithio phosphate (ZDDP) are known to increase thin-film friction. Though such additives may be required for other reasons such as to protect engine parts, the increase in thin-film friction caused by such additives can be detrimental.
Reducing boundary layer friction in engines may also enhance fuel efficiency. The motion of contacting surfaces in an engine may be retarded by boundary layer friction. Non-nitrogen-containing, nitrogen-containing, and molybdenum-containing friction modifiers are sometimes used to reduce boundary layer friction.
Rudnick, “Lubricant additives: chemistry and applications,” 2nd ed., Page 17, CRC Press, 2009 discloses that copper salts of mono-oxazoline or bis-oxazoline have improved varnish control and oxidation inhibition capabilities in lubricants.
U.S. Pat. No. 4,162,224 discloses a lubricating composition containing a reaction product of boric acid, substituted phenol and bis-oxazoline or oxazoline, where the oxazoline has formula:
where R is a straight, ranched chain or cycloalkyl group containing from 4 to 30 carbon atoms. The compound is said to impart a desired degree of antiwear and/or antioxidant protection to the lubricant composition. The patent contemplates using the lubricant composition for a machine or an engine.
U.S. Pat. No. 4,618,436 discloses a multifunctional lubricant composition comprising an internal acid phosphate salt of a borated oxazoline, where the oxazoline has formula:
where R is selected from about C8 to about C30 hydrocarbyl or
such as an acyl sarcosine-derived substituent or mixture thereof, at least one of R1, R2, R3, R4 is hydroxyalkyl having from 1 to about 6 carbon atoms and the remaining of R1, R2, R3, R4 are independently selected from the group consisting of C1 to about C30 hydrocarbyl, C1 to about C6 hydroxyalkyl, hydrogen or
where R8 is hydrogen or C1 to about C6 hydrocarbyl, or
or mixtures thereof, R5 is about C30 hydrocarbyl, R6 is C1 to about C6 hydrocarbyl and R7 is C1 to about C3 hydrocarbylene. The lubricant composition may also contain other components, such as corrosion inhibitors, extreme pressure agents, viscosity index improvers, co-antioxidants, other antiwear agents and the like. The lubricant composition is said to be capable of reducing the friction of an engine operating with oil in its crankcase.
U.S. Pat. No. 4,097,389 discloses a lubricant composition containing a borated product of a compound of the formula:
as a detergent, with the alkenyl group containing 1 to 30 carbon atoms. Other additives that may be used in the lubricant composition include other detergents, viscosity improvement agents, extreme pressure additives, and oxidation stability additives.
U.S. Pat. No. 4,035,309 discloses a lubricant composition comprising a reaction product that predominantly comprises a compound of formula:
where R is the hydrocarbyl group of succinic anhydride, and each X may represent a —CH3OH group. The lubricant composition may be used in automotive crankcase, automatic transmission fluids, or in petroleum fuels such as gasoline. Additional additives such as a viscosity index improver, a pour point depressant, or a zinc dialkyldithiophosphate antiwear agent may also be included in the lubricant composition.
In recent years there has been a growing desire to employ lubricants that provide higher energy-efficiency, especially lubricants that reduce friction by employment of friction modifiers in the lubricants. The present disclosure provides an improved lubricant composition that may reduce one or both of thin film friction and boundary layer friction.